All underground pipes which conduct liquid tend to act as habitats for organisms which multiply and form deposits. The deposits produce drag on the liquids and suspended solids in the pipe and impede flow. Changes in pipe direction may cause accumulations of solids which must be removed periodically.
Camera investigation generally precedes any cleaning operation. If a deposit is detected, a spray head fed by a water hose is lowered down the vertical access shaft into the horizontal pipe which contains the deposit. The access shaft is upstream of the deposit so that the pipe fall assists in carrying the flushed deposits downstream.
The water hose emits jets of water at mains pressure (4 bar) and as the hose is fed from a reel, the head retreats upstream dislodging deposits as it goes. When the section of pipe has been cleaned, the head is retrieved by exerting tension on the hose. During this recovery the hose turns the corner where the shaft meets the pipe and considerable abrasion occurs. The hose deteriorates and eventually becomes unfit for use and must be replaced. Even if the corners were chamfered or radiussed, the friction would be considerable because the head is heavy and if the water flow is maintained during recovery, the forces are substantial. The coefficient of friction between the polymer of the hose and the surface of the concrete is high and the operational life of the hose is unduly shortened.
U.S. Pat. No. 3,351,968 to Masters describes a hose guide for sewers and waste conduits consisting of a first frame of beams which span the manhole on the surface and support a central pulley which turns the entrant hose through about 90 degrees and passes it to a second frame which is subterranean and is lodged in the intersection between the vertical shaft beneath the manhole and the horizontal conduit to be cleaned. The second frame in Masters also has a central pulley which turns the hose through another 90 degrees. These keep the hose in the centre of the intersection in Masters and the vertical shaft and consequently no contact between the hose and the intersecting conduit wall occurs. Deployment of the frames in Masters requires extra time and labour and the second frame is an obstacle to the cleaning operations.
An attempt to dispense with pulleys is seen in U.S. Pat. No. 6,182,676 to Lee, wherein the mouth of the horizontal conduit is covered over part of its circumference with an arcuate pad which is scalloped to guide the hose around the corner at the mouth of the conduit.
Likewise when electric cables are fed into pits at the entry of a horizontal micro bore the cable must be fed from a reel on a vehicle above the pit and the cable must turn about 100 degrees to enter the micro bore. In mines, hydraulic hoses may have to turn corners to supply equipment working in shafts. The same problem emerges.